The prevalence of obesity has increased dramatically in the US over the last two decades, with rapidly rising and premature adverse health consequences. Women of reproductive age, especially minorities and those of low socioeconomic status, are at risk of adverse pregnancy outcomes due to excessive gestational weight gain (GWG) and this further contributes to alarming rates of childhood obesity and diabetes. Preventing excessive GWG could reduce pregnancy complications and improve long term health of women and their offspring. Weight control studies in pregnancy are emerging but most studies have emulated traditional weight control programs through diet counseling and/or increased activity with limited evidence of sustained adherence. Novel approaches are needed to limit weight gain to Institute of Medicine (IOM) goals, and to help new mothers adhere to recommended diet, physical activity and lifestyle behaviors they can model for their families. The proposed research will develop and test a new approach to primary and secondary prevention of obesity through a behaviorally adapted, nutrient-dense, energy-balanced lifestyle that can be implemented clinically, assessed objectively and sustained long term through technologically-advanced selfmonitoring methods. This randomized controlled clinical trial compares with standard care, the GWG of overweight / obese pregnant women who participate in lifestyle intervention with individualized, motivational coaching and group sessions to develop self-monitoring of recommended diet and physical activity behavior long term. Anthropometric, metabolic, diet, activity and lifestyle outcomes will be assessed prenatally and for at least 12 months post delivery. The Northwestern Department of Obstetrics and Gynecology provides care for over 12,000 ethnically diverse obstetric patients a year, many of whom participate in clinical trials, facilitated by a highly functional obstetric research infrastructure. Our multidisciplinary team, experienced in obstetrics and prevention research, propose innovative technology and enhanced self-monitoring skills to document whether new mothers can be better prepared to develop and model diet and energy-balanced lifestyle behaviors for their families and themselves and reduce and prevent obesity long term.